At this point, your subconscious will begin to collect a database of certain things that happen when you're dreaming. They'll probably be so small, you wouldn't even be able to consciously recognize them. They may be small things like the way your body reacts to something, a lack of a certain hormone in your blood, or something in the dream, like the way people speak, a lack of intellectual stimulation, etc. It will combine all of these and look for them. It's actually very similar to what we commonly refer to as intuition.